The use of non-azeotropic fluid mixtures in a heat pump, in order to improve the performance coefficient of the heat pump, has been the object of prior French patents and patent applications (Pat. Nos. 2 337 855, 2 474 151, 2 474 666 and No. 2 497 931 corresponding respectively to U.S. Pat. No. 4,089,186, U.S. Pat. No. 4,344,292, U.S. Pat. No. 4,350,020 and U.S. application Ser. No. 339,565).
More specifically, the French Pat. No. 2 474 151 describes non-azeotropic mixtures of two constituents capable of increasing the performances of a heat pump and thus, to decrease the operating cost of said heat pump. The two constituent mixtures described therein do not increase, however, the thermal power of a given compressor.
The object of the present invention is to show that specific fluid mixtures can be used to increase the thermal power delivered by a heat pump, as compared to the case where the same pump operates with a pure fluid. It is thus possible to reduce the investment cost by using the fluid mixtures of the invention in heat pumps. As a matter of fact the mixed working fluids of the invention result in an increase of the thermal capacity of a given heat pump, without modification of the parts of said heat pump, particularly without modification of the compressor.
Two conventional means are used to increase the thermal power of a heat pump; a first means consists of equipping the pump with a compressor of greater capacity, to thereby increase the drawn volume, but this technique increases the investment cost. The other means to increase the thermal capacity of a heat pump is to use a working fluid whose boiling point is lower than that of the conventional fluid. In fact, this substitution leads to a decrease of the performance coefficient and also to a narrower range of use of the pump, since the fluid of lower boiling point has generally a lower critical temperature.
The proposed invention concerns conventional applications of heat pumps, more particularly those wherein the usually employed working fluid is monochlorodifluoromethane (R 22; boiling point: -40.8.degree. C.) or dichlorodifluoromethane (R 12; boiling point: -29.8.degree. C.).
The above two fluids may be replaced, in conventional uses, with azeotropic mixtures of R 12 or R 22 with a halogen compound of close boiling point. These azeotropic mixtures have generally a boiling temperature slightly below that of R 12 or R 22 respectively and behave as pure fluids. Thus R 500, which consists of 73.8% b.w. of dichlorodifluoromethane R 12 (B.P.=-29.8.degree. C.) and 26.2% b.w. of difluoroethane R 152a (B.P.=-24.75.degree. C.), has a boiling point of -33.5.degree. C.; R 502, which consists of 48.8% b.w. of chlorodifluoromethane R 22 (B.P.=-40.8.degree. C.) and 51.2% b.w. of chloropentafluoroethane R 115 (B.P.=-38.7.degree. C.) has a boiling point of -45.6.degree. C. R 501, comprising 75% b.w. of chlorodifluoromethane R 22 and 25% b.w. of dichlorodifluoromethane R 12, whose boiling point (B.P.=-41.4.degree. C.) is very close to that of R 22, may also be mentioned.
The above-mentioned halogenated fluids are commonly employed in the heat pump installations used for heating or conditioning houses, for town heating and for low temperature industrial applications, such as certain operations of drying or concentration. The use of monochlorodifluoromethane (R 22) or of R 502 is quite common in the heat pumps used in house heating and making use, as a cold source, of underground water, water from wells or rivers, external air or extracted air, and, as heat source, of heating water or internal air, for temperatures which can reach 55.degree. C. at the heat source.
The substitution of R 502 to R 22 in a heat pump does not substantially increase the thermal capacity; however it allows a substantial decrease of the output temperature. The use of R 12 or R 500 is particularly well adapted to relatively high temperature levels, for example higher than 50.degree. C. and lower than 80.degree. C.